There has been heretofore proposed the use of a steel cord or a steel wire which is processed to have a flat coil shape, as a reinforcement material for a pneumatic tire (for example, see Japanese patent application Kokai publication Nos. Hei 10 (1998)-217716, Hei 10 (1998)-258609, and Sho 63 (1988)-96338). Such a reinforcement material having the flat coil shape has been processed to have a predetermined shape in the following manner. Specifically, a steel cord or a steel wire, which has a cylindrical coil shape, is squeezed from both sides by unvulcanized rubber while being crushed so as to fold respective loop portions in the coil-axis direction. As a result in the reinforcement material having the flat coil shape, a plurality of loop portions are arranged so as to be partly superposed on each other in sequence.
However, the above-described reinforcement material having the flat coil shape is processed while the cylindrical coil shape steel cord or the steel wire being squeezed. Thus, it is difficult to stabilize a shape of the material, and quality of a rubber product is made unstable. Moreover, since the above-described reinforcement material having the flat coil shape is embedded in the rubber product while retaining torsional stress, there may be adverse effects on fatigue resistance of the rubber product. Note that, in sandwiching the steel cord or the steel wire, which has the cylindrical coil shape, by use of unvulcanized rubber while squeezing the cord or the wire, it is required to complicate processing equipment thereof in order to reduce variation in quality. Thus, manufacturing costs of the rubber product are increased.